In manufacturing electronic devices, etching is performed to form a hole, a trench or the like in a silicon oxide film, which is an insulating layer. In general, the silicon oxide film is etched by exposing a target object to a plasma of a fluorocarbon gas as disclosed in U.S. Pat. No. 7,708,859.
In the etching using the plasma of the fluorocarbon gas, the silicon oxide film is etched by active species of fluorine. Further, in this etching, a deposit is formed by adhesion of fluorocarbon to the silicon oxide film.
In the above-described etching of the silicon oxide film, a film thickness of the deposit is gradually increased. When the film thickness of the deposit is increased, it becomes difficult that active species which serves to etch the silicon oxide film reach the silicon oxide film. Thus, the etching of the silicon oxide film is stopped in the middle of the processing. As a result, the etching rate of the silicon oxide film deteriorates.
The target object may have a first region of silicon oxide and a second region of silicon nitride. In that case, it is required to selectively etch the first region with respect to the second region of the target object. In the case of using the plasma of the fluorocarbon gas, a thickness of the deposit is greater on the second region than on the first region. Therefore, the etching rate can become higher in the first region than in the second region.
However, at an initial stage of the etching, a deposit is not formed on the second region. Therefore, the second region is etched at the initial stage of the etching.